This present invention relates to manufacture of electrochemical cells. More particularly, the present invention provides a method and system for recharging a solid state battery for related applications. Merely by way of example, the invention has been provided for the application of lithium based cells, but it would be recognized that battery cells of other materials such as zinc, silver, copper and nickel could be used in the same or like fashion. Additionally, such batteries can be used for a variety of applications such as portable electronics (cell phones, personal digital assistants, music players, video cameras, and the like), power tools, power supplies for military use (communications, lighting, imaging and the like), power supplies for aerospace applications (power for satellites), and power supplies for vehicle applications (hybrid electric vehicles, plug-in hybrid electric vehicles, and fully electric vehicles). The design of such batteries is also applicable to cases in which the battery is not the only power supply in the system, and additional power is provided by a fuel cell, other battery, IC engine or other combustion device, capacitor, solar cell, etc.
Commercial lithium ion batteries contain organic solvent-based liquid electrolytes, consisting of three main components: the lithium salt, the organic solvent, and the additives. These organic solvent-based liquid electrolytes are detrimental to battery's performance and safety due to the solvents' low boiling and flash points and auto-ignition temperatures, and the salt's low thermal stability and sensitivity to hydrolysis. For these reasons, lithium ion batteries using organic solvent-based liquid electrolytes have to be cycled under very tightly controlled conditions to limit the voltage ranges, limit the discharge/charge current, and lower the battery temperature (less than 60° C.). These stringent conditions prominently affect the design of charge methods, in particular, for these batteries. The desired objectives for recharging a battery should be maximizing energy and/or capacity utilization, maximizing energy efficiency and minimizing charge time. However, the priority of these desirable objectives is usually overtaken by improving safety and prolonging cycle life in designing charge methods for lithium ion batteries just because of organic solvent-based liquid electrolytes. Specifically, these organic solvent-based liquid electrolytes require the recharge method to use lower end-of-charge voltage limits, lower charge current and/or rates, and narrower state-of-charge ranges. Because of the voltage and state-of-charge limiting, not all the energy and/or capacity allowed by the battery electrochemistry are fully utilized.
For example, the Chevrolet Volt tightly control and buffer the on-board battery usage so that the battery only operates within a state-of-charge window of 65 percent. In other words, 5.6 kWh energy out of the designed 16 kWh total energy of the battery pack is not used at all. The voltage and charge rate limiting also adds to the sophistication and complexity of battery charging algorithms and systems. These problems are common for all the batteries using organic solvent-based liquid electrolytes for applications such as consumer electronics, grid storage, plug-in hybrid electric vehicles and battery electric vehicles.
From the above, it is seen that techniques for improving the charging methods and systems relating to solid state cells are highly desirable.